What exactly IS Alternative?

You know Nightlife, I've wondered the same thing. I looked it up on Wikipedia and it said something about Alternative being bands that didn't get much recognition but that still greatly influenced other bands and were very important to their genre. I guess it would make sense seeing how alternative means "to serve or used in a place of another." So I guess before Nirvana came along, Grunge music was considered alternative music. Weird huh? I have a feeling I will never understand this...